While the effects of age on the adrenergic responsiveness of cardiac ventricular tissue has been delineated, data is scanty on how age may affect the cholinergic modulation of these adrenergic effects. Neither adrenergic nor cholinergic modulation of aged atrial have been studied. Isolated transmural left atrials strips from adult (12 mo) and senescent (24) virgin male Wister rats were stimulated isometrically at Lmax at 30 C in krebs buffeer containing 0.5 mM Ca+. A dose response relationship to progressively greater concentration of isoproterenol 10 to the-12 to 10 to the-6M) was established for both groups. A progressive dose response relationship was similarly established for acetylcholine 10 to the-10 to 10 to the-3M) in atria superfused with Krebs already containing 10 to the-6 isoproterenol. Changes in time to peak force, total developed tension, resting tension, contraction duration, and maximal rate of force development were measured. While age-related changes in time to peak force and contraction duration were found, an initial analysis of the data failed to shown any age-related changes in adrenergic responsiveness as measured by these parameters. However, the developed tension in isoproterenol-potentiated senescent atria was more sensitive to suppression by acetylcholine.